In electrical inspection of a circuit board, it is conducted to measure an electric resistance between electrodes of an inspection object circuit board (hereinafter also referred to as “circuit board to be inspected”).
In the measurement of an electric resistance of a circuit board, there has heretofore been adopted, for example, a means in which probes PA and PD for current supply and probes PB and PC for voltage measurement are pressed against and brought into respective contact with 2 inspection object electrodes 81 and 82 (hereinafter also referred to as “electrodes to be inspected”), which have been electrically connected to each other in a circuit board 80 to be inspected, as illustrated in FIG. 15, a current is supplied between the proves PA and PD for current supply from a power supply device 83 in this state, and a voltage signal detected by the probes PB and PC for voltage measurement at this time is processed in an electric signal processor 84, thereby determining an electric resistance value between the electrodes 81 and 82 to be inspected.
In the method described above, however, the surfaces of the electrodes 81 and 82 to be inspected may be damaged by pressing the probes because it is necessary to bring the probes PA and PD for current supply and the probes PB and PC for voltage measurement into respective contact with the electrodes 81 and 82 to be inspected by considerably great pressing force, the probes are made of a metal, and the tips thereof are pointed, so that the circuit board becomes unusable. Under such circumstances, the electric resistance measurement cannot be carried out on all circuit boards to be provided as products, and so the method cannot help adopting the so-called sampling inspection, and after all, the yield of the products cannot be increased.
In order to solve such a problem, there have heretofore been proposed inspection apparatus in which a connecting member coming into contact with electrodes to be inspected is formed by an anisotropically conductive sheet (see, for example, Prior Art. 1 to Prior Art. 3).
According to such inspection apparatus, an electrode for current supply and an electrode for voltage measurement are brought into contact with electrodes to be inspected of a circuit board to be inspected through the anisotropically conductive sheet, whereby electrical connection is achieved, so that the measurement of electric resistance can be conducted without damaging the electrodes to be inspected.
As a certain kind of inspection apparatus which achieves electrical connection to electrodes to be inspected through an anisotropically conductive sheet, is used, for example, an apparatus of the construction that an upper-side board-compressing member 91A arranged on an upper surface side of a circuit board 1 to be inspected, on which upper-side electrodes 2 to be inspected are provided, and having an anisotropically conductive sheet 93A on its front surface (lower surface in FIG. 16), and a lower-side board-compressing member 91B arranged on a lower surface side of the circuit board 1 to be inspected, on which lower-side electrodes 3 to be inspected are provided, and having an anisotropically conductive sheet 93B on its front surface (upper surface in FIG. 16) are arranged so as to be opposed to each other in vertical direction as illustrated in FIG. 16.
In such an inspection apparatus (hereinafter also referred to as “first conventional apparatus”) 90, the upper-side board-compressing member 91A and lower-side board-compressing member 91B are respectively provided on base plates 96A and 96B supported by a plurality of supports 94A and 94B respectively infixed into flat plate-like support-infixing plates 95A and 95B and vertically extending from the support-infixing plates 95A and 95B, and as illustrated in FIG. 17, supporting points 97A formed by the supports 94A on the base plate 96A and supporting points 97B formed by the supports 94B on the base plate 96B on a plane M4 of projection in a thickness-wise direction of the base plates 96A, 96B when the first conventional apparatus 90 is seen through from above are located at the same positions. In FIG. 17, the supporting points (hereinafter also referred to as “upper-side supporting points”) 97A related to the upper-side board-compressing member 91A and the supporting points (hereinafter also referred to as “lower-side supporting point”) 97B related to the lower-side board-compressing member 91B are indicated by a black circle and a white circle, respectively.
In FIG. 16, reference numeral 92A designates a circuit board for inspection, on which electrodes for current supply and electrodes for voltage measurement (both not illustrated) making up pairs of inspection electrodes corresponding to the upper-side electrodes 2 to be inspected have been formed, reference character 92B designates a circuit board for inspection, on which electrodes for current supply and electrodes for voltage measurement (both not illustrated) making up pairs of inspection electrodes corresponding to the lower-side electrodes 3 to be inspected have been formed, reference numerals 98A and 98B designate electrode devices electrically connected to the respective circuit boards 92A and 92B for inspection and a tester (not illustrated), and reference numerals 99A and 99B designate anisotropically conductive sheets.
In this first conventional apparatus 90, the support-infixing plates 95A and 95B related to each of the upper-side board-compressing member 91A and lower-side board-compressing member 91B are moved in directions approaching to the circuit board 1 to be inspected, thereby pressing the base plates 96A and 96B by the supports 94A and 94B to compress the circuit board 1 to be inspected by the upper-side board-compressing member 91A and lower-side board-compressing member 91B. As a result, a measurable state is brought about. In this measurable state, the anisotropically conductive sheets 93A and 93B provided on the respective surfaces of the upper-side board-compressing member 91A and lower-side board-compressing member 91B are brought into contact with pressure with the respective electrodes to be inspected of the circuit board 1 to be inspected, whereby measurement of electric resistance is carried out by applying pressure to the respective electrodes to be inspected.
With respect to a printed circuit board for generally mounting integrated circuits or the like, it is necessary to confirm that a wiring pattern of the circuit board has the expected performance before the integrated circuits or the like are mounted. Therefore, the inspection of the electrical properties thereof is conducted. As an inspection apparatus for inspecting such a circuit board, there is known that having the construction that anisotropically conductive sheet is intervened between an inspection object circuit board and a plurality of inspection electrodes arranged in accordance with a pattern corresponding to inspection object electrodes of the inspection object circuit board to conduct the electrical inspection of the inspection object circuit board (see, for example, Prior Art. 4).
As a certain kind of inspection apparatus for such a circuit board, is used, for example, an apparatus having the construction that an upper-side board-compressing member 101A having a circuit board 102 for inspection, on which inspection electrodes 102A corresponding to upper-side electrodes 2 to be inspected of an inspection object circuit board (circuit board to be inspected) 1 have been formed, and a lower-side board-compressing member 101B having a circuit board 107 for inspection, on which inspection electrodes 107A corresponding to lower-side electrodes 3 to be inspected have been formed, which are arranged on an upper side having the upper-side electrodes 2 to be inspected and on a lower side having the lower-side electrodes 3 to be inspected in the circuit board 1 to be inspected, respectively, are arranged so as to be opposed to each other in vertical direction as illustrated in FIG. 18, and the upper-side board-compressing member 101A and lower-side board-compressing member 101B are respectively provided on base plates 106 supported by a plurality of supports 104 infixed into flat plate-like support-infixing plates 105 and vertically extending from the support-infixing plates 105.
In this inspection apparatus (hereinafter also referred to as “second conventional apparatus”) 100, anisotropically conductive sheets 103 are provided on the respective surfaces of the circuit boards 102 and 107 for inspection. In FIG. 18, reference numeral 108 designates electrode devices electrically connected to the respective circuit boards 102 and 107 for inspection and a circuit board for inspection of a tester (not illustrated), and reference numeral 109 designates anisotropically conductive sheet.
In this second conventional apparatus 100, the support-infixing plates 105 related to each of the upper-side board-compressing member 101A and lower-side board-compressing member 101B are moved in directions approaching to the circuit board 1 to be inspected, thereby pressing the base plates 106 by the supports 104 to compress the circuit board 1 to be inspected by the upper-side board-compressing member 101A and lower-side board-compressing member 101B. As a result, a measurable state is brought about.
In this second conventional apparatus 100, as with the first conventional apparatus 90, upper-side supporting points formed by the supports 104 on the base plate 106 related to the upper-side board-compressing member 101A and lower-side supporting points formed by the supports 104 on the base plate 106 related to the lower-side board-compressing member 101B on a plane of projection in a thickness-wise direction of the base plates when the second conventional apparatus 100 is seen through from above are located at the same positions.
In the conventional apparatus of the above-described construction, the anisotropically conductive sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in the thickness-wise direction when they are pressurized in the thickness-wise direction. Since the anisotropically conductive sheet has such features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it functions as a connector for achieving electrical connection making use of such features.
On the other hand, in recent years, the size and pitch or clearance of electrodes in a circuit board have tended to become small for the purpose of achieving a high degree of integration.
In an inspection apparatus for inspecting such a circuit board, that having a small thickness is used as the anisotropically conductive sheet for the purpose of exactly electrically connecting electrodes to be inspected of the circuit board to be inspected to inspection electrodes corresponding to the electrodes to be inspected. The anisotropically conductive sheet having the small thickness involves a problem that it cannot sufficiently absorb strain due to deflection caused to the base plate by being pressed by the supports, and so, in the measurable state, a scatter of pressure distribution tends to occur on the circuit board to be inspected to encounter difficulty in applying even pressure to the respective electrodes to be inspected of the circuit board to be inspected.
In the inspection apparatus having such a thin anisotropically conductive sheet, the inspection is conducted with great pressing force for applying pressure of at least a certain value to all the electrodes to be inspected of the circuit board to be inspected to achieve expected measurable state as to the respective electrodes to be inspected of the circuit board to be inspected, and so great pressure is also applied to the anisotropically conductive sheet at every inspection. Therefore, the anisotropically conductive sheet is liable to be deteriorated. As a result, a problem that inspection efficiency is lowered as the anisotropically conductive sheet is required to be frequently replaced in the inspection apparatus also arises.
In the inspection apparatus, it is thus investigated to make the thickness of the base plate greater for lessening the deflection of the base plate caused by pressing of the supports.
However, when the thickness of the base plate making up the inspection apparatus is made great, points of application of the pressing force applied to the circuit board to be inspected by the supports through the base plates and board-compressing members are formed at the same positions on a plane of projection in a thickness-wise direction of the board-compressing members when the inspection apparatus is seen through from above. The pressing force is thus concentrated on the points of application in the circuit board to be inspected, and so the pressing force at the points of application becomes greatest, and the pressing force at positions distant from the points of application becomes smaller as the distance from the points of application is greater. A scatter of pressure distribution is thus caused. As a result, a problem that a scatter of electrically connected state related to the electrodes to be inspected of the circuit board to be inspected is caused is involved. Another problem that the weight of the apparatus itself is increased by the increase in the thickness of the base plate is also involved.
When the thickness of base plates is made great in an inspection apparatus having the construction that through-holes are formed in the base plates, a problem that the step of forming the through-holes in the base plates becomes complicated in the production process thereof to lower productivity is also involved.
More specifically, when it is intended to form a through-hole in a thick base plate by one drilling operation, for example, a drill bit is liable to be damaged or broken. Therefore, the through-hole is generally formed by means of a method in which a concave hole is formed by conducting a drilling operation from one side of the base plate, and a drilling operation is also conducted from the other side of the base plate to form a concave hole so as to be linked to the first-mentioned concave hole. Since one through-hole is formed in such a manner, it is necessary to conduct the drilling operation plural times. It thus takes a long time to conduct the drilling operations, and moreover there is a possibility that the concave holes formed by the respective drilling operations may not be linked in an expected state, so that the through-holes cannot be formed with high efficiency.
Prior Art. 1: Japanese Patent Application Laid-Open No. 26446/1997;
Prior Art. 2: Japanese Patent Application Laid-Open No. 2000-74965;
Prior Art. 3: Japanese Patent Application Laid-Open No. 2000-241485;
Prior Art. 4: Japanese Patent Application Laid-Open No. 183974/1991.